Dental procedures have, for many years, involved several distinct kinds of surgical operations with differing purposes and effects. For example, dental procedures that most people undergo involve the removal from the tooth of a small portion thereof so as to remove dental caries that are effecting that tooth. The dental caries and at least a small portion of healthy tooth surrounding it are removed, the preparation that is thus produced is then ready to accept a filling, and the filling is then placed. A variety of drilling or cutting instruments are employed during such a procedure.
Another procedure that is not so common, but nonetheless may be practised by an ordinary family dentist at least several times each week during the conduct of his business, is the preparation of a tooth or teeth for subsequent placement of crowns, onlays, inlays, or veneers. Another related procedure is the precise preparation of a tooth to accommodate a clasp or rest of prescribed dimensions for a removable partial denture. For purposes of this discussion, all such related procedures--the removal of the surface or at least a portion of the surface of the tooth to prepare it for subsequent placement of an artificial substance--will be considered as being in respect of dental crown preparation.
Briefly, dental crown preparation requires the dentist to grind or otherwise remove a specific amount of the surface of the tooth. This procedure, reduction of the tooth, generally requires that the depth or amount of reduction shall be from about 0.5 mm to about 2.0 mm. This is not to say that the amount of reduction should vary on any one tooth in any one procedure--although that is possible; but it is to say that the amount of reduction may vary from tooth to tooth or procedure to procedure, depending on a number of circumstances that would be determined by the dentist at that time. Also, of course, the amount of reduction might be somewhat less for purposes of placement of an onlay or inlay, or possibly a veneer, as opposed to the amount of reduction that might be required for the placement of a crown or partial crown.
The dental procedures of grinding teeth, or cutting or abrading teeth, are generally carried out using rotationally driven cutting or grinding instruments, which in general might be classified as being dental burrs. In fact, the usual classification of armamentarium may comprise a variety of rotary instruments that might be specifically classified as stones, burrs, or drills. For example, the stones are used for abrading or wearing down the surface of the tooth such as by the use of fine diamond chips or dust that are cemented to a base. In a narrow definition, dental burrs may be considered to be miniature milling cutters, having a plurality of blades that shear away the tooth structure from the tooth surface and where the cutting blades are disposed along the sides of the instrument. Drills, specifically twist drills, have their cutting edges at the tips of the instrument, and are generally intended only so as to bore a small diameter hole into the tooth structure. However, for purposes of this discussion, all of the above instruments may be generally considered to be dental burrs, and this will be especially so in the following discussion which proposes several alternative surface treatments or geometries for dental burr structures that are otherwise in keeping with the present invention.
When dental crown preparation is being undertaken, the dentist first determines how much surface reduction should be made. Then, the portion of the tooth surface, if not the entire tooth surface, is marked so as to determine the boundaries within which the procedure will be undertaken if it is not over the entire surface of the tooth. Tooth reduction then begins, and it is at this point that dental burrs according to the present invention will be used.
When a crown procedure is being undertaken, the general steps include tooth reduction, and then an impression of the remaining tooth is taken and sent to a dental prosthetics laboratory. The laboratory then fabricates the crown, having made a model of the impression, and having been informed of the desired prosthesis type, they must assume that accurate reduction and/or preparation has been accomplished by the dentist to permit said prosthesis fabrication. In other words, the dental prosthetics laboratory has in its hands a model of the tooth after the reduction has been made, and it is then required to build a crown to be cemented to the remaining portion of the tooth and to restore the depth of reduction that has been prepared by the dentist. The crown is then fabricated and returned to the dentist for placement in the mouth, usually a few days or a week or so after the tooth reduction has been taken.
A more complete discussion of the dental burrs used in the initial, depth gauging steps of tooth reduction and crown preparation techniques and procedures, will be found in companion application Ser. No. 08/162,958, filed Dec. 8, 1993 in the name of the present inventor, and relating to DENTAL BURRS; of which application the present application is a C-I-P. Those dental burrs are the ones used in the most difficult step taken in crown preparation--that is the maintenance of a constant depth of reduction, once it has been determined as to how much reduction should occur. If the depth of reduction has not been constant, or has been more or less than advised by the prosthetic technical specifications, then the crown may not fit or it may not replicate the previous tooth structure which it replaces. The manner by which the depth of the reduction is to be determined may vary slightly among dentists, but not significantly. When a dentist is preparing the tooth for tooth reduction, he first cuts a series of grooves into the tooth. Almost invariably, the series of grooves is cut into the tooth using a long cutting burr that may be cylindrical, or which may be slightly tapered, but in any event the groove is cut into the surface of the tooth by placing the burr lengthwise against the tooth and pressing it into the tooth along the length of the burr while the burr is rotating. This creates a groove that is as long as the burr or at least the portion of the burr that is in contact with the surface of the tooth. But the depth of the groove is difficult to determine; and the usual practice is essentially to gauge the diameter of the burr and then sink the burr into the surface of the tooth for one-half of its diameter--or in some cases, its full diameter. After several grooves are placed into the surface of the tooth, then the remaining tooth material between the grooves is ground or abraded away, until the depth of the grinding or abrading of the material reaches the same depth as the grooves that have been previously cut into place by the side of a burr as noted above.
The steps preceding the cutting of a plurality of grooves into the surface of the tooth, and the steps of removing the tooth's structure between the grooves after they have been put in place, would remain essentially the same for any dentist who uses the dental burr of the present invention, as previously. However, the step of placing the grooves into the surface of the tooth, so as to determine the boundaries of the tooth reduction procedure if an entire reduction is not taking place and the placement of intermediate depth grooves where gross reduction is taking place, are easily and extremely accurately undertaken using the dental burr of the present invention. Of course, even when an entire crown is to be placed, meaning that the entire surface of the tooth is to be reduced, there still remains a boundary at the gingival area of the tooth, where the shoulder of the crown to be placed meets the remaining structure of the tooth at, near, or below the gumline.
What the present invention provides is a dental burr whose purpose is to cut a groove into the tooth structure, where the groove has a specific and predetermined depth. As noted above, the depth of the groove to be cut into the tooth may only be as little as 0.5 mm in some cases, or it may be as much as 2.0 mm in other cases. Also, as noted above, the depth of the groove should be uniform, because the dental prosthetics laboratory assumes that a constant depth of reduction has occurred over prescribed tooth areas for which the laboratory is fabricating the crown or other dental prosthetic.
There are, of course, several reasons for the concern as to the accuracy of the depth of the grooves that are initially placed in the tooth structure as part of the dental crown procedure. They include among them the fact that, if the depth of the groove is either too much or too little, then the dental prosthetic that has been prepared by the laboratory may not fit--in that it would not necessarily replicate the tooth structure that it replaces. If less reduction has occurred than the respective restorative dentistry specifications dictate, then it is possible that a crown might not go into place because its resultant laboratory fabrication would be overcontoured and thereby interfere with the adjacent tooth or teeth. If more reduction has occurred than has been prescribed by restorative dentistry specifications, then the vitality of the tooth may be jeopardized by the stated over-reduction.
It should be noted that, a final impression is only made after the reduction procedure has taken place. Preliminary impressions that are made prior to the tooth reduction procedure are taken in order to mould a temporary crown or restoration that is put into place for cosmetic and functional purposes, which crown or restoration is generally one that is fabricated by the dentist in his own office.
Of course, if the tooth reduction has been inaccurately done, then unhappiness may occur between the patient and the dentist, and/or between the dentist and the dental prosthetic laboratory. This could mean unwarranted and unnecessary delays in time, additional time in the chair by the patient--for which the patient may be quite unwilling to pay the dentist--and sometimes it may require re-fabricating the dental prosthetic, the cost for which may have to be absorbed by the dentist or the laboratory. When the depth of the initial depth gauge grooves are accurately determined and placed, then none of the above difficulties would arise.
A further purpose to which the methods of the present invention may be put is the preparation of onlay or inlay to cover or encapsulate existing silver amalgam that is already in place in a tooth structure. Recently, there has been some concern raised about the mercury component of silver-amalgam--a material that has been used over a long period of time as fillings in teeth after removal of dental caries--becoming systemic within the body of the patient. By employing the present invention, the existing silver-amalgam can be reduced a sufficient amount that an enamel, gold, or other dental material onlay or inlay may be emplaced. The chance of mercury release and/or chelation into the body of the patient has been shown to be much greater due to grinding, attrition, or fracture of the silver-amalgam filling, and escape of mercury into the mouth, than the likelihood of mercury becoming systemic in the body of the patient through the root structure of the tooth. Thus, conventional onlay or inlay techniques may be employed to cover or encapsulate the remaining silver-amalgam after reduction; and it is evident that reduction using the process and methods of the present invention ensures an economical and effective onlay or inlay. Indeed, as at the filing date of this Application, silver-amalgam restorations are not allowed in Sweden. Thus, the methods of the present invention can be used to define and remove a portion of the silver-amalgam restoration from a tooth, so that no trauma is caused to the otherwise healthy tooth.